P16286 [Lanqiao Cup 2026 NOI Qualifier Python A Group] Voltage Scheduling

A scheduling center is responsible for voltage scheduling for $N$ parallel power transmission cables in a city. These cables are numbered from $1$ to $N$ from left to right. Initially, the output voltage of all cables is $0$ kV. To meet the electricity demand of different areas, cable $i$ must finally be stabilized at voltage $v_i$ kV. To achieve this, the scheduling center is equipped with an “interval voltage boosting device”: it can be activated once per day. Each time, an engineer may choose any continuous interval $[L, R]$ ($1 \leq L \leq R \leq N$), and increase the output voltage of all cables in this interval by $1$ kV at the same time. Given the target voltage sequence $v_1, v_2, \cdots, v_N$, compute the minimum number of days needed to make the voltage of each cable reach exactly its corresponding target value.

The first line contains an integer $N$, indicating the number of power transmission cables. The second line contains $N$ integers $v_1, v_2, \cdots, v_N$, where $v_i$ indicates the target voltage (in kV) that the $i$-th cable needs to reach.

Output one integer in one line, indicating the minimum number of days required to make the voltages of all cables reach exactly the target values.

### Constraints For $30\%$ of the testdata, $1 \leq N \leq 10^3$. For $100\%$ of the testdata, $1 \leq N \leq 10^5$, $0 \leq v_i \leq 10^9$. Translated by ChatGPT 5